Tandem repeats of nucleotide sequences are found throughout the human genome and are sufficiently unique to an individual that these repeating sequences can be used in human or other organism identification. These markers are also useful in genetic mapping and linkage analysis. The sequences are important for determining, for example, predisposition for disease, disease diagnosis, and human identity, such as in forensics analysis. There are many types of tandem repeats of nucleic acids, including variable number tandem repeats (e.g., minisatellites and microsatellites). Microsatellites include short tandem repeats (STRs).
One application of tandem repeat analysis is in forensics or human identity testing. In current forensics analyses, highly polymorphic STRs are identified using a DNA sample from an individual and DNA amplification steps, such as polymerase chain reaction, to provide amplified samples of partial DNA sequences, or amplicons, from the individual's DNA. The amplicons can then be matched by size (i.e. repeat numbers) to reference databases, such as the sequences stored in national or local DNA databases. For example, amplicons that originate from STR loci can be matched to reference STR databases, including the FBI CODIS database in the United States, or the NDNAD database in Europe, to identify the individual by matching to the STR alleles specific to that individual.